This invention relates generally to illumination arrangements for instrument dials and more particularly to an improved illumination arrangement for a dial of an analog timepiece, such as a wristwatch in a preferred embodiment.
It is known to provide instruments such as wristwatches with a light source for illuminating the dial. The wristwatch dial may be an analog wristwatch dial having indicia or markers used in combination with hands of the wristwatch, or the dial may comprise an electro-optic display of actuated indicia, such as a liquid crystal display. It is both an objective and challenge in any dial illumination arrangement to achieve a constant and uniform lighting of the dial. Uniform background lighting may be achieved by using a distributed uniform light source, such as an electroluminescent light source. However, in order to reduce the cost of an illumination system for a dial, concentrated light sources, such as a single incandescent bulb or a light emitting diode (LED), have also been considered. One problem with using a concentrated light source is to effectively transfer and diffuse the point source of bright light to a uniformly distributed light for illuminating the dial. The prior art contains many examples of such efforts.
For example, U.S. Pat. Nos. 3,748,456; 2,140,972; 2,188,821; 2,480,393; 3,043,038; and 3,561,145 are examples of prior art constructions for illuminating dials. U.S. Pat. Nos. 4,250,575 and 6,682,201 as well as GB 2 052 114; JP2004-279098; JP2006-226867 and JP2008-111848 are also examples of varying prior art examples of dial illumination arrangements.
However, the state of the art has perceived deficiencies. For example, the distribution of light has been found to be less than uniform. Second, there can be significant non-uniformity of illumination nearest the lamp or other light source. Third, there is also perceived deficiencies where such light sources are mounted and positioned in the prior art. For example, an advantage of the present invention is the positioning of the concentrated light source on the rear side of the dial, for example, mounted on the printed circuit board, while the light itself is required on the front side of the dial. Moreover, prior art examples of concentrated light sources are known to create light spots, which is also less than desirable. Although known solutions in the prior art include the use of multiple light sources, this too is less than desirable for obvious reasons.
It can therefore be seen that it has been particularly difficult to effectively and uniformly conduct light from a concentrated source located beneath the watch dial through a light guide and out of the light guide above the dial. Space within the timepiece is also an important criterion to consider, and previously known constructions have also been less than satisfactory in this regard.
Another example of a light guide for illuminating a dial is described in U.S. Pat. No. 6,183,099, but here too, the present inventors believe that improvements can be made. This U.S. Pat. No. 6,183,099 also itself cites numerous prior art examples of dial illumination assemblies.
Accordingly, an improved illumination arrangement for a dial of a timepiece, and a wristwatch in particular, that overcomes the drawbacks found in the prior art while at the same time provides for a desirable and uniform distribution of illumination, is desired.